They can ban for absolutely anything they feel like. If they don't think you're a valuable asset to them, they can ban you and call it just about anything. They're incredibly vague.
They definitely favor "old" accounts over newbies. For instance, lots of "old" accounts got away with self-hosting ripped images while newbies were getting bans. But, once again, it comes down to rather Amazon sees your website as an asset, or just a way to shave off a % of a sale they were already making.
I would highly, highly suggest keeping your informational content to product review at a 5:1. I would also never write a product review shorter than 500 words. That's just my opinion of course. But if you're paranoid about getting a ban, don't risk having an obvious micro-affiliate website with crap reviews.